Tyres

Abstract: A tire with reduced tread noise includes a tread having a plurality of base pitches (20A-J) arranged about the circumference of the tire in at least one pitch sequence. Each base pitch in the pitch sequence has a tread geometry defined by a plurality of load-supporting tread blocks (40A-E) separated or interrupted by grooves (47,49) and/or sipes (48). The base pitches in the pitch sequence have various tread geometries, to reduce the noise of the tire on the road surface. The grooves and/or sipes in each base pitch have common end points (60,61) along the leading and trailing edges of the base pitches such that the grooves and/or sipes are continuous across the boundary between adjacent base pitches in the pitch sequence. Likewise, the grooves and/or sipes in each base pitch in one rib or row in the tire can have common end points along the edge between a base pitch in an adjacent rib or row, such that the grooves and/or sipes are continuous in the lateral direction as well. The base pitches formed in this manner can be arranged in a particular pitch sequence regardless of: (i) the individual tread geometry of each base pitch, or (ii) the particular sequence of base pitches. Moreover, the length of the base pitches in the circumferential direction can also be varied by known manners (e.g., random, sinusoidal) to further reduce the noise of the tire on a road surface.

Description: The present invention relates generally to tyres, in particular to tyre treads, and is especially concerned with the selection of novel tread dispositions with a view to achieving low tyre tread noise. BACKGROUND The tread of a modern tyre extends around the outer circumference of the tyre and is designed to contact the road surface. The tread is typically divided into a plurality of raised, load-supporting tread blocks separated by intersecting circumferential and transverse grooves and/or sipes. The tread blocks determine the control, acceleration and braking characteristics of the tyre, while the grooves and/or sipes are necessary to provide flexibility and water removal. The tread blocks are typically arranged in "base pitches" around the tire, wherein each base pitch includes a predetermined geometry of whole and/or partial tread blocks separated by grooves and/or sipes. Each tread block in the base pitch may be separated from the other tread blocks by circumferential grooves, transverse grooves, and/or grooves which extend in other selected directions. Likewise, the tread blocks can be separated or interrupted by circumferential sipes, transverse sipes, and/or sipes which extend in other selected directions, as is known to those skilled in the art. In other words, each base pitch has a particular tread geometry which is chosen by the designer at least in part according to the factors outlined above. Additionally, each base pitch may vary in width across the tyre. For example, each base pitch may extend transversely from one shoulder to the other shoulder of the tyre. Alternatively, there may be several rows or ribs of base pitches, each of which extends transversely over only a single circumferential section or partial axial extent, e.g. over a single rib or combination of ribs. In any case, the base pitches are repeated around the circumference of the tyre to form the complete tyre tread. The constant contact of the tyre tread with the road surface during use can often create unwanted noise. In particular, as the tyre contacts the road surface, the individual tread blocks cause air disturbances upon impact with the road, creating a spectrum of audio frequencies broadly referred to as "tire noise". The following factors contribute to tyre noise: (1) the impact of the tread block on the road surface; (2) the vibration of the tyre carcass; and (3) the "air pumping" which occurs as the tread blocks become compressed and expand into the grooves separating adjacent blocks. Various tread designs have been developed which attempt to reduce the noise of the tread on the road surface. Such noise treatment techniques attempt to distribute the noise frequency produced by the tyre tread over a wide frequency band to approach what is termed "white noise". For example, one known technique for reducing tread noise is to use base pitches having different pitch lengths, wherein the "pitch length" is a measure of the length from the leading edge of one base pitch to the leading edge of the next adjacent base pitch in the circumferential direction of the tyre. Lippman et al in US-A-2,878,852 disclose a tyre tread having male and female mold halves, wherein each mold half has a separate pitch sequence extending around the circumference of the tyre. Lippman discloses a pitch sequence which is represented by the series of relative circumferential distances: 9 10 11 12 10 11 12 13 12 11 10 9 11 12 13 10 10 13 12 11 9 10 11 12 13 12 11 10 12 11 10 9. These circumferential distances represent the relative circumferential length of successive tread units expressed in any desired measuring unit. In Lippman the tread units are selected to be mirror images of themselves or of other groups in each respective mold half. Another technique for reducing tyre tread noise is described in our earlier-filed EP-A-542493. This specifies certain pitch length criteria for arranging the base pitches relative to each other in the pitch sequence to reduce the noise of the tyre. FR-A-2205423/US-A-3861436 describes a tyre tread with a circumferential sequence of tread sections whose tread geometry varies with the aim of resisting wear, reducing high speed tyre noise and maintaining good traction in various road surface and weather conditions. The illustrated treads include circumferential grooves which extend continuously around the tyre with a zig-zag of constant width. Other techniques use random or sinusoidal sequencing of the pitches in an attempt to modulate the objectionable noise-producing frequencies and spread the tyre noise over a broad frequency spectrum (see e.g., Vorih, US-A-3,926,238). It is noted that the documents acknowledged above disclose varying the pitch length of each base pitch according to certain criteria. Accordingly, the above references disclose certain techniques which are designed to reduce noise produced by the tyre tread when contacting the road surface. However, there is a constant demand in the industry for new and improved techniques for providing a tyre with lower tyre tread noise, and in particular, techniques which can be used in addition to, or alternatively to, the techniques described above for providing a tyre which gives a low tyre tread noise on the road surface. The aim herein is therefore to provide new proposals for tyre tread design, particularly with a view to achieving low tread noise, and preferably distributes the noise of the tyre tread over a broad frequency range. The tyre of this invention has a tread with axially-spaced circumferential shoulders and a tread pattern of tread pattern elements, namely load-supporting tread blocks separated by grooves and/or sipes, between the shoulders. The tread pattern is divisible, by lateral boundaries extending across the tread parallel to the tyre axis, into a circumferentially-extending sequence of base pitches, each base pitch having a pattern cell of tread pattern elements. At least one tread pattern element in each base pitch is a circumferentially-extending groove or sipe that intersects the lateral boundary of the base pitch, the intersection being at an axial position between the tyre shoulders that is the same for all the base pitches in the sequence so that there is continuity of said circumferentially-extending grooves or sipes with those of adjacent base pitches across the lateral boundaries, and would be such continuity regardless of the ordering of the base pitches in the sequence. There are at least three different base pitch pattern cells, distinguished from one another by differing distances of lateral divergence of their respective circumferentially-extending grooves or sipes within the cell from said axial position. Further, the grooves and/or sipes of the base pitches preferably have common end points along the boundary-between base pitches in adjacent rows or ribs, such that the grooves and/or sipes of the tread which cross adjacent base pitches in the lateral direction of the tyre do not abruptly end, but rather are also continuous across the base pitches in the adjacent rib or row. Accordingly, the base pitches can be arranged in any sequence around the circumference of the tyre, regardless of the different tread geometries of the base pitches, and regardless of the particular arrangement of base pitches. The different tread geometries of the base pitches distribute the noise of the tyre over a broad frequency range and thereby reduce the noise of the tread on a road surface. The final design of the tyre tread is determined significantly or primarily by the different base pitch tread geometries which provide the greatest reduction in tyre tread noise, although e.g. variation in length of the base pitches in the circumferential direction of the tyre may also be a factor. Furthermore, this technique can be used in addition to, or alternatively to, other noise reduction techniques to reduce the noise of the tyre on the road surface, such as by varying the length of the base pitch in the circumferential direction of the tyre using sinusoidal or random sequences, or by other known techniques or methods. The base pitches in a given sequence around the tyre may be related to one another by sharing in common some basic geometry elements (of groove and/or sipe layout), the variation in geometry prescribed by the present proposals being achieved by more specific changes in the layout. Further options, preferred features and their effects will be understood from the following description of examples. Reference is made to the accompanying drawings in which: Fig. 1 is a perspective view of a tyre embodying the present proposals; Fig. 2 is a schematic illustration of a tyre tread design, and Fig. 3 is a schematic illustration of another tyre tread design. Referring to the drawings, and initially to Fig. 1, a tyre, indicated generally at 10, includes a tyre tread, indicated generally at 15, which extends around the circumference of the tyre. The tyre is designed to rotate around an axis "R" during contact with the road surface. Generally, the tyre is preferably a radial tyre. However, the present proposals are not necessarily limited to any particular tyre type, size or style. Rather, they may be applied to any type of tyre having a tread. The techniques for manufacturing and forming such tyres are known to those skilled in the tyre art and will not be discussed herein. As shown in Fig. 2, a tyre tread 15 includes a plurality of base pitches, for example base pitches 20A-20J. In this example the tread has 88 base pitches around the circumference. The base pitches have five different pitch lengths (labelled 1, 2, 3, 4, 5) arranged e.g. in the following sequence: 2344233334113132325331331222 322112445532343114355132323214425135344445545415151511 222115. For this pitch sequence, the following ratios of pitch lengths can be used and labeled as follows: 0.7488- 0.8410- 0.9348- 1.0280- 1.1220- for the above blocks labelled 1, 2, 3, 4, 5, respectively. Each base pitch 20A-20E in the tread preferably extends transversely from the inside shoulder 28 to the center line 29 of the tyre tread to form a bottom half 30, while base pitches 20F-20J extend from centerline 29 to the opposite shoulder 31 to form a top half 32. However, as indicated previously, each base pitch could also extend transversely across only a portion of the tyre, for example across one circumferential section (or rib) of the tyre, or across the entire width (i.e., from shoulder 28 to the opposite shoulder 31) of the tyre. Each base pitch 20A-20E includes an arrangement of whole and/or partial load-supporting tread blocks. For example, base pitch 20C at least partially includes tread blocks 40A-40E spread across base pitch. The tread blocks are separated or interrupted by grooves and/or sipes to form the tread pattern. For example, tread blocks 40C and 40E are separated by circumferential groove 45, while tread blocks 40A and 40B are separated by transverse groove 47. Further, sipe 48 extends inwardly toward the centerline of the tyre from circumferential groove 49 and at least partially bisects tread block 40D. Additionally, sipe 50 extends outwardly away from the centerline of the tyre from circumferential groove 49 and at least partially bisects tread block 40B. The circumferential and transverse grooves and/or sipes can be relatively straight (e.g., such as circumferential groove 45), or can be curved or bent (e.g., such as circumferential groove 49), as is generally known by those skilled in the art. Moreover, the grooves and/or sipes in each base pitch can extend in other than circumferential and transverse directions across the tread block (e.g., such as groove 51 in base pitch 20E which extends in an arc), and can extend between adjacent grooves, can originate and terminate at the same groove, or can cross the boundary of adjacent base pitches (such as circumferential groove 49). In other words, the tread geometry of each base pitch can comprise any predetermined geometry of tread blocks, grooves and sipes, and can be based on any prescribed criteria for producing a tread pattern, such as block stiffness, noise, handling, wear, and/or stone removal, e.g. as currently known to those skilled in the art. Certain of the base pitches around the circumference of the tyre have different tread geometries. In particular, the arrangement of whole and/or partial tread blocks, and the location of the grooves and/or sipes in each base pitch, varies around the tyre according to certain criteria, as will be described more fully herein. As used herein, the term "tread geometry" relates to the particular arrangement of tread blocks, grooves and/or sipes within each base pitch; while the term "tread pattern" relates to the tread design of the entire tyre tread. The tread pattern of the tyre has a number of different tread geometries which it has been determined reduce the noise of the tyre on the road surface. Note however that the base pitches 20A-E have basic geometry elements in common, forming effectively a "pattern cell". Here, each has inner straight circumferential groove portion 45, outer curved circumferential groove portion 49 and inward and outward lesser "branch" grooves extending laterally from groove 49 to the shoulder and from groove 49 to groove 45. A tyre constructed according to this technique has low tread noise because the noise of the tyre is spread across a broad frequency range. It is believed that by having base pitches with different tread geometries, cyclical vibrations are prevented from occurring, as the harmonics caused by the impact of the tyre tread on the road surface, the vibration of the carcass, and air pumping, are spread across a broad frequency range. However, for traction and wear reasons, it is important that the grooves and/or sipes in the tread be continuous around the tyre, particularly in the circumferential direction, and not abruptly terminate across adjacent base pitches because of any different tread geometries between the base pitches. Therefore. according to preferred principles proposed herein, to the extent that any groove and/or sipe extends across adjacent base pitches, such groove(s) and/or sipe(s) has common edge points along the leading and trailing edges of each base pitch, regardless of the geometry of the remainder of the base pitch. Accordingly, the grooves and/or sipes in each base pitch which extend to an edge(s) of the base pitch are matched to a groove and/or sipe, respectively, in an adjacent base pitch. The base pitches can thereby be arranged in any particular sequence relative to each other, regardless of the different geometries of the base pitches and regardless of the particular pitch sequence employed, and still maintain continuity of the grooves and/or sipes across adjacent base pitches. For example, base pitches 20A-20D in Figure 2 all have different tread geometries. Circumferential groove 49 in the bottom half 30 of the tyre tread extends across base pitches 20A-20E. At the boundary between the base pitches, the groove 49 has common end points across each base pitch. For example, groove 49 has end points 60A, 60B on the leading edge of base pitch 20C which match end points 61A, 61B on the trailing edge of adjacent base pitch 20D. Further, groove 49 in base pitch 20D has end points 63A, 63B on the leading edge of base pitch 20D which match end points 64A, 64B on the trailing edge of adjacent base pitch 20E. The matching of the end points continues from base pitch to base pitch around the tyre tread. As should be apparent, the end points for groove 49 are located at the same location along both edges of each base pitch. For example, if an end point of groove 49 along the leading edge of a base pitch is one (1) inch from the sidewall, then a corresponding end point of the groove 49 along the trailing edge of the base pitch is also one (1) inch from the sidewall. Using this technique, the base pitches can be arranged relative to each other in any desired sequence. For example, base pitch 20C could also be located adjacent base pitch 20E, in either the leading or trailing direction, with the groove 49 extending continuously across the boundary between these base pitches. It should also be apparent that although groove 49 is illustrated as extending across the entire length of each base pitch, it is possible that the groove could also be interrupted across the base pitch. In particular, the groove could extend from one edge of the base pitch and terminate along the shoulder or centerline of the tyre, or terminate at another groove. Meanwhile, another groove could extend from the opposite edge (at the same location) and also terminate at the centerline or shoulder, or at another groove in the tyre. Various other alternatives are also contemplated, as long as the end points of the grooves along the leading and trailing edges of the base pitches are at the same location such that when the base pitches are located in adjacent relation to each other (regardless of which sequence is chosen), the grooves are continuous across the boundary between the base pitches. This technique may also be applied to sipes which extend across adjacent base pitches. In other words, to the extent that any sipes cross adjacent base pitches, the sipes are formed such that they terminate at the same location along the leading and trailing edges of the base pitches. Thus, regardless of the particular arrangement of base pitches in the pitch sequence, or the tread pattern of any particular base pitch, the grooves and/or sipes are continuous across the base pitches. Another tread pattern formed according to the present principles is shown in Figure 3. In this tread pattern, the tyre has 65 base pitches. The base pitches have three different pitch lengths (i.e., 1, 2, 3) arranged in the following sequence: 311233332111312211333212331112312111231132233323113213 12221333123. For this pitch sequence, the following ratios of the pitch lengths can be used and labeled as follows: 0.9988- 1.2958- 1.6198 for the above blocks labeled 1, 2, 3, respectively. Base pitches 70A-70D are illustrated as extending from shoulder 72 to the centerline 73 of the tyre. Additional base pitches 70E-70H extend from the centerline 73 to the opposite shoulder 75 in the upper half 76. Again, it will be noted that the base pitches in the bottom half 74 have grooves and/or sipes at the same location along the leading and trailing edges of each base pitch, such that the base pitches can be arranged in any manner. For example, base pitch 70C has a different tread geometry from base pitch 70D. Circumferential groove 77 has end points 78A, 78B on the trailing edge of base pitch 70D at the same location as end points 79A, 79B on the leading edge of base pitch 70C. Thus, the base pitches can be arranged in any sequence and have continuity across the leading and trailing edges of the base pitches. According to a further aspect of the present proposals, the grooves and/or sipes that extend across the edges between base pitches in adjacent circumferential rows or ribs also have common end points such that there is continuity laterally across the tyre tread as well. For example, as shown in Figure 3, groove 81 extends across the centerline 73 between base pitch 70B in the bottom half 74 and base pitch 70F in the upper half 76 of the tyre. In this case, each base pitch in one row or rib preferably has the same length in the circumferential direction as a corresponding base pitch in the adjacent row or rib. In other words, the pitch sequences in the adjacent rows or ribs are the same. The base pitches may also be arranged such that the leading and trailing edges of the base pitches in one circumferential row or rib match the leading and trailing edges of the base pitches in the adjacent row or rib. In any case, the grooves and/or sipes are continuous laterally across the centerline around the entire tyre tread. Continuity can also thus be maintained in the lateral direction of the tyre by forming the grooves and/or sipes between ribs or rows of base pitches with common end points in the same manner as continuity is achieved in the circumferential direction described previously. Nevertheless, some tyre tread designs have relatively wide circumferential grooves separating adjacent rows or ribs of base pitches (see, e.g., circumferential groove 45 in Fig. 2), and thus this technique might not be necessary for this type of tyre as the benefits in wear and traction are not as significant. In any case, one particularly advantageous aspect of the present proposal is that the principles can be easily applied to known techniques for reducing tyre tread noise. For example, the techniques such as discussed in our earlier-filed EP-A-542493 may be used additionally. In these techniques the base pitches in the pitch sequence(s) are arranged relative to each other according to certain pitch length criteria to reduce the noise of the tyre on the road surface. It is within the scope of the present proposals to have a different tread geometry (such as described above) for each base pitch with a different pitch length in the pitch sequence(s). Because the edges between base pitches have grooves and/or sipes with common edge points according to our preferred teachings, the base pitches can be arranged in any selected arrangement while maintaining continuity across the boundary between base pitches. One useful pitch sequence for a tyre tread having three pitch lengths is represented by the following sequence of relative pitch lengths: 332233113112311311212121333 231332331112122233131213321212113312232121333211223311 1233113. For this pitch sequence, the following ratios of pitch lengths can be used and labeled as follows: 1.00-1.25-1.50 for the above blocks numbered 1, 2, 3, respectively. Again, even though the base pitches may have different tread geometries based upon the pitch lengths of the base pitches, all the base pitches have common edge points, and thus can be arranged in any manner and still maintain continuity across the boundary of the base pitches. Of course, the pitch sequence described above is only exemplary in nature, and the broad proposal is not limited to any particular pitch sequence. Further, other techniques could be used to reduce the tyre tread noise. For example, each base pitch around the circumference of the tyre can have a different tread geometry of tread blocks and grooves and/or sipes. However, for manufacturing purposes, it is preferred that the tread pattern be limited to between three and seven different tread geometries. As will be appreciated by those skilled in the art upon reading and understanding the principles disclosed here, by having different tread geometries about the circumference of the tyre, the frequency produced by the base pitches will be spread across a broad range. Tests have been run with tyre treads which had base pitches formed and arranged in pitch sequences according to the principles disclosed here. The base pitch geometry in the tyre treads varied according to pitch length variation (i.e., each base pitch with a particular pitch length had its own base pitch geometry). Upon comparing these tyres with tyres wherein the base pitches varied in length, but otherwise had the same geometry, it was found that the harmonics produced by the tyres formed according to the present principles were flatter and broader than in the control tyres. In other words, there were fewer peaks and valleys in the harmonic spectrum. Further, although overall tyre tread noise was found to be about the same for all tyres tested at speeds less than 30 miles per hour, the noise was reduced at speeds greater than 30 miles per hour. Accordingly, the present teachings provide a simple, yet useful technique for reducing tyre noise which can be used on a wide variety of commercially available tyres, and as an alternative or in addition to the particular pitch sequence employed.

Claims: A tyre with a tread (15) having axially-spaced circumferential shoulders (28,31) and a tread pattern of tread pattern elements, namely load-supporting tread blocks (40A-E) separated by grooves (45,47,49) and/or sipes (48,50), between the shoulders; the tread pattern being divisible, by lateral boundaries extending across the tread parallel to the tyre axis, into a circumferentially-extending sequence (30,32) of base pitches (20A-E, F-J), each base pitch having a pattern cell of tread pattern elements and at least one tread pattern element in each base pitch being a circumferentially-extending groove (49) or sipe that intersects the lateral boundary of the base pitch, the intersection being at an axial position (60,61(A,B);63,64(A,B)) between the tyre shoulders that is the same for all the base pitches in the sequence (30,32) so that there is continuity of said circumferentially-extending grooves (49) or sipes with those of adjacent base pitches across the lateral boundaries, and would be such continuity regardless of the ordering of the base pitches in the sequence; there being at least three different base pitch pattern cells, characterized in that the pattern cells are distinguished from one another by differing distances of lateral divergence of their respective said circumferentially-extending grooves or sipes within the cell from said axial position. A tyre according to claim 1 in which the tread pattern is divisible by one or more circumferential boundaries into plural said circumferentially-extending sequences of such base pitches extending round the tyre side-by-side, grooves and/or sipes in the base pitches of one sequence having continuity across the circumferential boundary thereof with grooves and/or sipes in the base pitches of the adjacent sequence. A tyre according to claim 1 or claim 2 in which different base pitch pattern cells have different circumferential lengths. A tyre according to any one of claims 1 to 3 in which each said circumferentially-extending groove (49) or sipe extends continuously across the respective base pitch from one of its lateral boundaries to the other. A tyre according to any one of the preceding claims in which there are not more than seven different base pitch pattern cells.

Inventors: WILLIAMS THOMAS ALAN, WILLIAMS, THOMAS ALAN
Applicants: CONTINENTAL GENERAL TIRE INC, CONTINENTAL GENERAL TIRE, INC.
Application year: 1994
Main classification: B60C11
IPC codes: B60C11, G10K11